1. Field of the Invention
This invention pertains to portable straight edge cutting guides for use with portable power tools, and in particular to that type of cutting guide in which the tool moves reciprocally along an elongated straight edge by means of a bearing block assembly, and having means to change to other types of tools. In this particular invention the straight edge cutting guide assembly is secured to and supported by the workpiece.
2. Description of the Prior Art
The problem of making precise cuts and grooves in a workpiece is faced by every craftsman. A number of straight edge cutting guides are disclosed in the prior art for use in a shop or with large size power tools. However, the prior patent art and commercially available products provide little help to the craftsman working on a site where he has to use portable power tools such as a router, a circular saw, a sabre saw or the like.
Several previous examples of guiding apparatus for power tools power for the tool to be held in a fixed position, usually with the cutting blade extending upward, and for the workpiece to be moved across the blade. The orientation of the workpiece with respect to the blade must be maintained by continuously pressing the workpiece firmly against a mechanical stop, while simultaneously directing it toward the blade. If sufficient force is not maintained against the stop, or if the workpiece suddenly lurches forward due to the forces generated by the rapidly spinning blade, the workpiece can move away from the stop, causing non-uniformity in the straightness of the cut or ever irreparable damage. In addition, the exposed upwardly projecting cutting blade presents a definite safety hazard to the operator.
U.S. Pat. Nos. 3,869,951 and 3,979,987 were attempts at an apparatus in which the workpiece is held fixed, and the tool is moved along its surface by means of a movable fixture which fastens to the tool and which rides along a track which defines the straight edge. However in both cases, the movable fixture has a U-shaped receptacle or groove which accepts the track. In such a construction there must be a tight enough fit between the receptacele and the track to insure an unwavering straight line as the fixture is moved, yet there also must be sufficient clearance between the two contacting surfaces to minimize the drag caused by their sliding against one another. The tremendous amounts of dust created by the cutting operator will build up on the track and fill this clearance space, thereby increasing the drag. This causes uneven movement of the fixture, intermediate binding, and lack of overall control over the cutting operation, i.e. the operator feels the friction due to this mechanism rather than the more important sensation of the cutting blade progressing through the workpiece. Even lubricants on the track do not alleviate this problem but rather increase the adhesion of dust particles to the track and actually contribute to the problem.
The closest prior patent to the present invention is U.S. Pat. No. 3,979,987 which discloses a cutting guide for portable power tools. This device has two major limitations. First, its adapter plate and wedge combination will not accept all type of power tools commercially available. The present invention is designed to accept a variety of adapter plate corresponding to the variety of tools available. Second, the vertical metal flange and the inverted U-shaped carrier show provide too much metal-to-metal contact which can easily be jammed with sawdust or fine metallic particles, interferring with the operation of the device. The present invention solves this problem with the provision of three cam follower bearings which grip the vertical flange of the straight edge cutting guide assembly while minimizing metal-to-metal contact.